a. Field of the Invention
This invention relates to a beam deflecting device to deflect a beam for irradiation onto a beam irradiating member. More particularly, the invention is concerned with a beam deflecting device having a beam detector to detect a position of the beam as deflected.
b. Description of Prior Arts
In a device for producing information outputs by scanning a beam irradiating member with a deflected beam, there is usually provided a beam detector in one part of a beam scanning path to render constant the position of the information output on the beam irradiating member. In other words, the starting position of the information output is determined by commencing modulation of the beam by an information signal in synchronism with a time, in which the beam is detected by the beam detector.
In the beam deflecting device using such beam detector, as the beam is detected in the above-described manner, a beam generator is so controlled that the beam may be emitted therefrom when the beam deflected by the deflector passes near-by the beam detector. With the beam deflecting device constructed as such, the beam detection signal output is produced at a predetermined time interval from the beam detector so far as the beam deflecting device operates regularly. By monitoring the time interval of this beam detection signal, therefore, it is possible to ascertain whether the beam deflecting device is operating regularly, or not. However, in the system of monitoring the time interval of the beam detection signal by emitting the beam only during a predetermined time period as mentioned above, a spurious beam detection signal is may be formed by noises, etc. to result in generation of an error signal, whereby accurate reinstating function cannot be imparted to the beam detector. For example, there exists a certain time period having no direct bearing on the recording operation after an information output is produced on one page until further information output is produced on a subsequent page, and also, in a state of waiting for an output, there is a time period which has no direct bearing on the recording operation. In case the abovementioned monitoring system is employed, if a spurious beam detection signal is detected during such time period, there is inevitably generated an error signal.